Longest mammal migration ever recorded measures in at 14,000 miles

And the remarkable journey is raising questions about the status of a critically endangered whale species.

In a study using satellite-monitored tags to track three western gray whales, a team of U.S. and Russian researchers recorded a stunning round-trip trek of 14,000 miles. The trio traveled from their primary feeding ground off of Sakhalin Island in Russia across the Pacific Ocean and down the west coast of California to Baja, Mexico and back home again.

One of the whales, dubbed Varvara by the scientists, visited the three major breeding areas for eastern gray whales, which are found off North America.

For a long time it was believed that western gray whales had gone extinct, but a small group was discovered in Russia off Sakhalin Island; they now number around 150 individuals and have been monitored by scientists from Russia and the U.S. since the 1990s. Meanwhile, populations of eastern gray whales were also in a tight spot, but conservation efforts have brought them back – today they are believed to have a population of some 18,000.

But here’s why Varvara’s visit to the eastern gray whales is interesting. Not all experts believe that the two species are in fact distinct, separate species. A number of scientists have proposed that western and eastern gray whale populations are not isolated and that the gray whales found in Russian waters are a part of an eastern population that is restoring its former range.

"The fact that endangered western gray whales have such a long range and interact with eastern gray whales was a surprise and leaves a lot of questions up in the air," said Bruce Mate, director of the Marine Mammal Institute at Oregon State University and lead author on the study. "Past studies have indicated genetic differentiation between the species, but this suggests we may need to take a closer look."

"The ability of the whales to navigate across open water over tremendously long distances is impressive and suggests that some western gray whales might actually be eastern grays," Mate said. "But that doesn't mean that there may not be some true western gray whales remaining.

He adds, "If so, then the number of true western gray whales is even smaller than we previously thought."

Does this spell doom for the western whales? Protecting them has proven challenging. Five western grays have perished in Japanese fishing nets within the last 10 years and their feeding grounds off Japan and Russia include fishing areas, shipping corridors, and oil and gas production – as well as future sites oil sites. But with this new research, hopefully fresh data and visibility will inspire some momentum in conservation efforts. With so few of these wandering giants left, and maybe even fewer than we thought, the time is now.